Records of production for 1168 cows were obtained from six herds tested in Dairy Herd Improvement Associations in Virginia for this study. The records were corrected to a mature equivalent basis, converted to four per cent fat-corrected milk, and averaged for each of the 862 cows used in the 89 families in the six herds. Each group of cows with three or more consecutive generations with records of production were identified and called “families”. The original cow in each family was called the “foundation cow”. The statistical analysis of the data for milk production, reproductive efficiency, and longevity was made by the method of analysis of variance. Significant differences between families were observed in Herd 4 and Herd 6 for milk production; however, when the data were classified by sire and by family, the variability between sires was highly significant and the variability between families was not significant. The other four herds did not exhibit any significant family differences. Only Herd 4 showed any significant difference between families for reproductive efficiency; the differences between families for the remaining five herds were not significant. No significant differences for longevity were observed between families in any of the six herds. Average relationship within a family was estimated for each family in a herd. In this study, average relationship within families ranged from 15 per cent for 34 animals in Herd 6 to 52 percent for 6 animals in Herd 5. Herd 2, Herd 4, and Herd 5 had higher within family relationship values than the remaining three herds. The herds with high family relationship values used inbreeding and linebreeding to concentrate the relationship within the families while the remaining three herds use sires not so closely related. Reproductive efficiency for the six herds ranged from 12.2 months to 14.5 months calving intervals, with an average of 15..9 months for all herds. Longevity for the six herds ranged from 6.4 years to 5.5 years with an average of 7.5 years for all herds. / M.S.